Abstract 1390: Inhibition of the catalytic activity of hUNG2 sensitizes multiple cancer cell lines to 5-FdUrd killing

Previously reported shRNA knockdown studies have established that expression of the DNA repair enzyme human uracil DNA glycosylase (hUNG2) is protective against 5-flourodeoxyuridine (5FdUrd) cell killing in p53 mutated cancer cell lines, but not in cell lines with functional p53. Here we take a different approach to understanding the role of hUNG2 in 5FdUrd chemotherapy by selectively inhibiting the catalytic activity of hUNG2 using the small bacterial inhibitor protein UGI. UGI binds extremely tightly to the DNA binding and catalytic site of hUNG2, effectively mimicking the impact of a small molecule inhibitor and allowing us to explore the potential therapeutic vulnerabilities that loss of hUNG2 activity produces in p53 mutated and wild-type cancer cells. Accordingly, we used lentiviral transduction to introduce UGI, under control of a doxycycline-inducible promoter, into a large panel of cancer cell lines. In vitro hUNG2 activity measurements using cell extracts established that all lines had robust activity before induction of UGI and undetectable activity after induction. We find that some wild-type and mutant p53 cancer lines from different tissues show significant increases in drug sensitivity. For instance, the p53 wild-type MCF7 breast cancer line showed a 10,000-fold increase in sensitivity, while the p53 mutant HT29 colorectal cancer line showed a 50-fold increased sensitivity. Overall, the results do not support the proposal that p53 status itself determines whether a cancer cell will be sensitized to 5FdUrd in the presence of hUNG2 inhibition. Ongoing studies are focused on identifying the cellular factors that contribute to drug sensitivity under conditions of hUNG2 inhibition. Realizing the full therapeutic benefit of 5FdUrd requires identification of the cancer cell phenotypes that are sensitized upon hUNG2 inhibition. Citation Format: Eric S. Christenson, Junru Cui, Anthony Gizzi, Mesfin Meshesha, James T. Stivers. Inhibition of the catalytic activity of hUNG2 sensitizes multiple cancer cell lines to 5-FdUrd killing [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1390.